第14章 ディレクトリー サーバー

14.1. OpenLDAP

LDAP (Lightweight Directory Access Protocol) is a set of open protocols used to access centrally stored information over a network. It is based on the X.500 standard for directory sharing, but is less complex and resource-intensive. For this reason, LDAP is sometimes referred to as 「X.500 Lite」.

Like X.500, LDAP organizes information in a hierarchical manner using directories. These directories can store a variety of information such as names, addresses, or phone numbers, and can even be used in a manner similar to the Network Information Service (NIS), enabling anyone to access their account from any machine on the LDAP enabled network.

LDAP is commonly used for centrally managed users and groups, user authentication, or system configuration. It can also serve as a virtual phone directory, allowing users to easily access contact information for other users. Additionally, it can refer a user to other LDAP servers throughout the world, and thus provide an ad-hoc global repository of information. However, it is most frequently used within individual organizations such as universities, government departments, and private companies.

This section covers the installation and configuration of OpenLDAP 2.4, an open source implementation of the LDAPv2 and LDAPv3 protocols.

14.1.1. Introduction to LDAP

Using a client/server architecture, LDAP provides reliable means to create a central information directory accessible from the network. When a client attempts to modify information within this directory, the server verifies the user has permission to make the change, and then adds or updates the entry as requested. To ensure the communication is secure, the Secure Sockets Layer (SSL) or Transport Layer Security (TLS) cryptographic protocols can be used to prevent an attacker from intercepting the transmission.

Mozilla NSS の使用法

The OpenLDAP suite in Fedora 16 no longer uses OpenSSL. Instead, it uses the Mozilla implementation of Network Security Services (NSS). OpenLDAP continues to work with existing certificates, keys, and other TLS configuration. For more information on how to configure it to use Mozilla certificate and key database, refer to How do I use TLS/SSL with Mozilla NSS.

The LDAP server supports several database systems, which gives administrators the flexibility to choose the best suited solution for the type of information they are planning to serve. Because of a well-defined client Application Programming Interface (API), the number of applications able to communicate with an LDAP server is numerous, and increasing in both quantity and quality.

14.1.1.1. LDAP の用語

The following is a list of LDAP-specific terms that are used within this chapter:

エントリー

A single unit within an LDAP directory. Each entry is identified by its unique Distinguished Name (DN).

属性

Information directly associated with an entry. For example, if an organization is represented as an LDAP entry, attributes associated with this organization might include an address, a fax number, etc. Similarly, people can be represented as entries with common attributes such as personal telephone number or email address.

An attribute can either have a single value, or an unordered space-separated list of values. While certain attributes are optional, other are required. Required attributes are specified using the objectClass definition, and can be found in schema files located in the /etc/openldap/slapd.d/cn=config/cn=schema/ directory.

The assertion of an attribute and its corresponding value is also referred to as a Relative Distinguished Name (RDN). Unlike distinguished names that are unique globally, a relative distinguished name is only unique per entry.

LDIF

The LDAP Data Interchange Format (LDIF) is a plain text representation of an LDAP entry. It takes the following form:

The optional id is a number determined by the application that is used to edit the entry. Each entry can contain as many attribute_type and attribute_value pairs as needed, as long as they are all defined in a corresponding schema file. A blank line indicates the end of an entry.

14.1.1.2. OpenLDAP 機能

OpenLDAP suite provides a number of important features:

LDAPv3 Support — Many of the changes in the protocol since LDAP version 2 are designed to make LDAP more secure. Among other improvements, this includes the support for Simple Authentication and Security Layer (SASL), Transport Layer Security (TLS), and Secure Sockets Layer (SSL) protocols.

LDAP Over IPC — The use of inter-process communication (IPC) enhances security by eliminating the need to communicate over a network.

IPv6 Support — OpenLDAP is compliant with Internet Protocol version 6 (IPv6), the next generation of the Internet Protocol.

LDIFv1 Support — OpenLDAP is fully compliant with LDIF version 1.

Updated C API — The current C API improves the way programmers can connect to and use LDAP directory servers.

Enhanced Standalone LDAP Server — This includes an updated access control system, thread pooling, better tools, and much more.

表14.2 一般的にインストールされる追加の LDAP パッケージの一覧

パッケージ

説明

nss-pam-ldapd

A package containing nslcd, a local LDAP name service that allows a user to perform local LDAP queries.

mod_authz_ldap

A package containing mod_authz_ldap, the LDAP authorization module for the Apache HTTP Server. This module uses the short form of the distinguished name for a subject and the issuer of the client SSL certificate to determine the distinguished name of the user within an LDAP directory. It is also capable of authorizing users based on attributes of that user's LDAP directory entry, determining access to assets based on the user and group privileges of the asset, and denying access for users with expired passwords. Note that the mod_ssl module is required when using the mod_authz_ldap module.

これらのパッケージをインストールするには、以下の形式で yum コマンドを使用します:

yuminstallpackage…

たとえば、基本的な LDAP サーバーのインストールを実行するには、シェルプロンプトにおいて root として以下のように入力します:

yum install openldap openldap-clients openldap-servers

Note that you must have superuser privileges (that is, you must be logged in as root) to run this command. For more information on how to install new packages in Fedora, refer to 「パッケージのインストール」.

14.1.2.1. OpenLDAP サーバーユーティリティの概要

To perform administrative tasks, the openldap-servers package installs the following utilities along with the slapd service:

表14.3 OpenLDAP サーバーユーティリティの一覧

コマンド

説明

slapacl

属性の一覧へのアクセス権を確認できます。

slapadd

LDIF ファイルから LDAP サーバーにエントリを追加できます。

slapauth

認証と認可の権限に対して ID の一覧を確認できます。

slapcat

Allows you to pull entries from an LDAP directory in the default format and save them in an LDIF file.

slapdn

Allows you to check a list of Distinguished Names (DNs) based on available schema syntax.

slapindex

Allows you to re-index the slapd directory based on the current content. Run this utility whenever you change indexing options in the configuration file.

slappasswd

Allows you to create an encrypted user password to be used with the ldapmodify utility, or in the slapd configuration file.

slapschema

Allows you to check the compliance of a database with the corresponding schema.

slaptest

LDAP サーバー設定を確認できます。

For a detailed description of these utilities and their usage, refer to the corresponding manual pages as referred to in 「インストールされているドキュメント」.

Make sure the files have correct owner

Although only root can run slapadd, the slapd service runs as the ldap user. Because of this, the directory server is unable to modify any files created by slapadd. To correct this issue, after running the slapd utility, type the following at a shell prompt:

With the exception of ldapsearch, each of these utilities is more easily used by referencing a file containing the changes to be made rather than typing a command for each entry to be changed within an LDAP directory. The format of such a file is outlined in the man page for each utility.

14.1.2.3. 一般的な LDAP クライアントアプリケーションの概要

Although there are various graphical LDAP clients capable of creating and modifying directories on the server, none of them is included in Fedora. Popular applications that can access directories in a read-only mode include Mozilla Thunderbird, Evolution, or Ekiga.

14.1.3. OpenLDAP サーバーの設定法

By default, the OpenLDAP configuration is stored in the /etc/openldap/ directory. The following table highlights the most important directories and files within this directory:

表14.5 List of OpenLDAP configuration files and directories

パス

説明

/etc/openldap/ldap.conf

The configuration file for client applications that use the OpenLDAP libraries. This includes ldapadd, ldapsearch, Evolution, etc.

/etc/openldap/slapd.d/

The directory containing the slapd configuration.

Note that OpenLDAP no longer reads its configuration from the /etc/openldap/slapd.conf file. Instead, it uses a configuration database located in the /etc/openldap/slapd.d/ directory. If you have an existing slapd.conf file from a previous installation, you can convert it to the new format by running the following command as root:

slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d/

The slapd configuration consists of LDIF entries organized in a hierarchical directory structure, and the recommended way to edit these entries is to use the server utilities described in 「OpenLDAP サーバーユーティリティの概要」.

Do not edit LDIF files directly

An error in an LDIF file can render the slapd service unable to start. Because of this, it is strongly advised that you avoid editing the LDIF files within the /etc/openldap/slapd.d/ directly.

14.1.3.1. 全体設定の変更方法

Global configuration options for the LDAP server are stored in the /etc/openldap/slapd.d/cn=config.ldif file. The following directives are commonly used:

olcAllows

The olcAllows directive allows you to specify which features to enable. It takes the following form:

表14.7 利用可能な olcDisallows オプション

Disables the enforcing of an anonymous session when the STARTTLS command is received.

tls_authc

Disallows the STARTTLS command when authenticated.

例14.4 Using the olcDisallows directive

olcDisallows: bind_anon

olcIdleTimeout

The olcIdleTimeout directive allows you to specify how many seconds to wait before closing an idle connection. It takes the following form:

olcIdleTimeout: number

このオプションはデフォルトで無効にされています（つまり、0 に設定されています）。

例14.5 olcIdleTimeout ディレクティブの使用法

olcIdleTimeout: 180

olcLogFile

The olcLogFile directive allows you to specify a file in which to write log messages. It takes the following form:

olcLogFile: file_name

The log messages are written to standard error by default.

例14.6 olcLogFile ディレクティブの使用法

olcLogFile: /var/log/slapd.log

olcReferral

The olcReferral option allows you to specify a URL of a server to process the request in case the server is not able to handle it. It takes the following form:

olcReferral: URL

このオプションはデフォルトで無効にされています。

例14.7 olcReferral ディレクティブの使用法

olcReferral: ldap://root.openldap.org

olcWriteTimeout

The olcWriteTimeout option allows you to specify how many seconds to wait before closing a connection with an outstanding write request. It takes the following form:

olcWriteTimeout

このオプションはデフォルトで無効にされています（つまり、0 に設定されています）。

例14.8 olcWriteTimeout ディレクティブの使用法

olcWriteTimeout: 180

14.1.3.2. データベース固有の設定の変更法

By default, the OpenLDAP server uses Berkeley DB (BDB) as a database back end. The configuration for this database is stored in the /etc/openldap/slapd.d/cn=config/olcDatabase={1}bdb.ldif file. The following directives are commonly used in a database-specific configuration:

olcReadOnly

The olcReadOnly directive allows you to use the database in a read-only mode. It takes the following form:

olcReadOnly: boolean

It accepts either TRUE (enable the read-only mode), or FALSE (enable modifications of the database). The default option is FALSE.

例14.9 Using the olcReadOnly directive

olcReadOnly: TRUE

olcRootDN

The olcRootDN directive allows you to specify the user that is unrestricted by access controls or administrative limit parameters set for operations on the LDAP directory. It takes the following form:

olcRootDN: distinguished_name

It accepts a Distinguished Name (DN). The default option is cn=Manager,dn=my-domain,dc=com.

例14.10 Using the olcRootDN directive

olcRootDN: cn=root,dn=example,dn=com

olcRootPW

The olcRootPW directive allows you to set a password for the user that is specified using the olcRootDN directive. It takes the following form:

olcRootPW: password

It accepts either a plain text string, or a hash. To generate a hash, use the slappaswd utility, for example:

例14.11 Using the olcRootPW directive

The olcSuffix directive allows you to specify the domain for which to provide information. It takes the following form:

olcSuffix: domain_name

It accepts a fully qualified domain name (FQDN). The default option is dc=my-domain,dc=com.

例14.12 Using the olcSuffix directive

olcSuffix: dc=example,dc=com

14.1.3.3. Extending Schema

Since OpenLDAP 2.3, the /etc/openldap/slapd.d/ directory also contains LDAP definitions that were previously located in /etc/openldap/schema/. It is possible to extend the schema used by OpenLDAP to support additional attribute types and object classes using the default schema files as a guide. However, this task is beyond the scope of this chapter. For more information on this topic, refer to http://www.openldap.org/doc/admin/schema.html.

14.1.4. Running an OpenLDAP Server

This section describes how to start, stop, restart, and check the current status of the Standalone LDAP Daemon. For more information on how to manage system services in general, refer to 7章サービスおよびデーモン.

14.1.4.1. Starting the Service

To run the slapd service, type the following at a shell prompt as root:

systemctl start slapd.service

If you want the service to start automatically at the boot time, use the following command:

systemctl enable slapd.service

Refer to 7章サービスおよびデーモン for more information on how to configure services in Fedora.

14.1.4.2. Stopping the Service

To stop the running slapd service, type the following at a shell prompt as root:

systemctl stop slapd.service

To prevent the service from starting automatically at the boot time, type:

systemctl disable slapd.service

Refer to 7章サービスおよびデーモン for more information on how to configure services in Fedora.

14.1.4.3. サービスの再起動方法

実行中の slapd サービスを再起動するには、シェルプロンプトにおいて root として以下のように入力します:

systemctl restart slapd.service

これにより、サービスが停止し、再び起動します。設定を再読み込みするためにこのコマンドを使用します。

14.1.4.4. サービスの状態の確認方法

サービスが実行中であるかどうかを確認するには、シェルプロンプトにおいて以下のように入力します:

systemctl is-active slapd.service

14.1.5. システムが OpenLDAP を使用して認証を実行するように設定する

In order to configure a system to authenticate using OpenLDAP, make sure that the appropriate packages are installed on both LDAP server and client machines. For information on how to set up the server, follow the instructions in 「OpenLDAP 製品群のインストール」 and 「OpenLDAP サーバーの設定法」. On a client, type the following at a shell prompt as root:

yum install openldap openldap-clients nss-pam-ldapd

8章認証の設定 provides detailed instructions on how to configure applications to use LDAP for authentication.

14.1.5.1. 古い認証情報を LDAP フォーマットへ移行

The migrationtools package provides a set of shell and Perl scripts to help you migrate authentication information into an LDAP format. To install this package, type the following at a shell prompt as root:

yum install migrationtools

This will install the scripts to the /usr/share/migrationtools/ directory. Once installed, edit the /usr/share/migrationtools/migrate_common.ph file and change the following lines to reflect the correct domain, for example:

For more information on how to use these scripts, refer to the README and the migration-tools.txt files in the /usr/share/doc/migrationtools-version/ directory.

14.1.6. その他のリソース

The following resources offer additional information on the Lightweight Directory Access Protocol. Before configuring LDAP on your system, it is highly recommended that you review these resources, especially the OpenLDAP Software Administrator's Guide.

14.1.6.1. インストールされているドキュメント

The following documentation is installed with the openldap-servers package:

/usr/share/doc/openldap-servers-version/guide.html

A copy of the OpenLDAP Software Administrator's Guide.

/usr/share/doc/openldap-servers-version/README.schema

A README file containing the description of installed schema files.

Additionally, there is also a number of manual pages that are installed with the openldap, openldap-servers, and openldap-clients packages:

クライアントアプリケーション

man ldapadd — Describes how to add entries to an LDAP directory.

man ldapdelete — Describes how to delete entries within an LDAP directory.

man ldapmodify — Describes how to modify entries within an LDAP directory.

man ldapsearch — Describes how to search for entries within an LDAP directory.

man ldappasswd — Describes how to set or change the password of an LDAP user.

man ldapcompare — Describes how to use the ldapcompare tool.

man ldapwhoami — Describes how to use the ldapwhoami tool.

man ldapmodrdn — Describes how to modify the RDNs of entries.

サーバーアプリケーション

man slapd — Describes command line options for the LDAP server.

管理アプリケーション

man slapadd — Describes command line options used to add entries to a slapd database.

man slapcat — Describes command line options used to generate an LDIF file from a slapd database.

man slapindex — Describes command line options used to regenerate an index based upon the contents of a slapd database.